1. Field of the Invention
The present invention relates to an aqueous ink composition and an image forming method.
2. Description of the Related Art
An aqueous active radiation-curable ink, i.e., an ink composition that contains water as the main medium and is curable upon irradiation with active radiation such as ultraviolet radiation, can be suitably used for image printing, pretreatment for imparting printing suitability to recording media, post-treatment such as protection or decoration of printed images, or the like. Further, since water is used as the main component, this type of ink composition is highly safe. In recent years, there is demand for forming a high quality image that cures at high sensitivity by using an aqueous active radiation-curable ink as an ink composition for inkjet recording.
However, an aqueous active radiation-curable type ink that satisfies stability over time, dischargeability or the like, which are necessary for ink in inkjet recording, and is capable of forming a cured film that exhibits excellent color saturation, print density, scratch resistance, fixability, marker resistance or the like, by irradiation with light, has yet to be achieved.
Use of various kinds of pigment dispersant polymers is known in terms of enhancing the properties of ink used for inkjet recording. For example, an ink in which a polymer having a benzene ring that is not directly linked to the main chain, as a pigment dispersant, is disclosed (see, for example, Japanese Patent Application Laid-Open (JP-A) No. 2009-84494), and this ink is said to exhibit excellent stability over time, dischargeability or the like. Furthermore, a crosslinkable composition in which a benzyl dimethyl ketal water-soluble photoinitiator is used and a styrene/acrylic acid/ethyl acrylate copolymer is used as a dispersant, is disclosed as an aqueous active radiation-curable ink (see, for example, JP-A No. 2008-247940), and this ink is said to exhibit high curing sensitivity.
However, since the ink described in JP-A No. 2009-84494 does not contain a polymerizable compound or the like and does not undergo a process such as photocuring, it may be difficult to say that the printed material obtained by using this ink has sufficient scratch resistance, fixability, marker resistance or the like.
Furthermore, the aqueous ink solution described in JP-A No. 2008-247940 may not exhibit sufficient ink stability, dischargeability or dispersibility, and the color saturation or print density of the cured film may not be satisfactory.
In view of the above, it is an object of the invention to provide an aqueous ink composition that is capable of forming a cured film that exhibits high print density, as well as excellent color saturation, scratch resistance, fixability and marker resistance. It is also an object of the invention to provide an image forming method in which this aqueous ink composition is used.